The OpenBSD box is a dedicated firewall that protects the internal network. Attached to the first switch(the switch that is attached to the border router) are my servers. So the servers are protected by the border router's firewall and their own firewalls, and access to the internal network, and between the servers and the internal network, is controlled by the OpenBSD box.
It took me a while to put dd-wrt on the border router so that this set-up is supported. The only questions i now have are:
1)would it be best to just bring up the OpenBSD's internal interface statically and to bring up the interfaces of machines on the internal subnet statically also. So that the OpenBSD box isn't doing dhcp for the internal network, it is just a firewall for it?
2)In which case should i have the border router as the DNS server for all the machines on the whole network?
3)Or would it be better for the machines on the internal network to get their I.Ps via dhcp, from the OpenBSD box(bearing in mind that the servers already get their I.Ps via dhcp from the border router) and have the OpenBSD as the DNS server for the internal network also?

Thank you for your time and any replies you might send
regards unixjingleman

would it be best to just bring up the OpenBSD's internal interface statically and to bring up the interfaces of machines on the internal subnet statically also. So that the OpenBSD box isn't doing dhcp for the internal network, it is just a firewall for it?

For such a small network, the benefits of separating the DHCP server from the firewall is negligible. This has been discussed before.

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In which case should i have the border router as the DNS server for all the machines on the whole network?

I tend to doubt that your border router is acting as a DNS server. I suspect it is relaying DNS received from your ISP.

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Or would it be better for the machines on the internal network to get their I.Ps via dhcp, from the OpenBSD box(bearing in mind that the servers already get their I.Ps via dhcp from the border router) and have the OpenBSD as the DNS server for the internal network also?

You are mixing two different subjects together. Separate them.

Whatever box serves DHCP is up to you.

Hosting DNS yourself only has value if you have your own unique domain. Otherwise, take advantage of whatever your ISP provides.

There are no magic or definitive answers to your questions. If this were a large corporate network, separation of functionality would have greater importance, but deciding what machine will serve what functionality in such a small network is all a matter of personal choice & opinion. Why don't you experiment & decide what is best for your environment?